Technical Field
The present invention relates to a mapping table accessing method, and more particularly, to a physical-logical mapping table accessing method for a rewritable non-volatile memory module, and a memory control circuit unit and a memory storage device using the same.
Description of Related Art
The growth of digital cameras, mobile phones, and MP3 players has been rapid in recent years. Consequently, the consumers' demand for storage media has increased tremendously. In recent years, a rewritable non-volatile memory has become an import part of the electronic industries because the rewritable non-volatile memory is capable of providing features such as data non-volatility, low power consumption, small volume, non-mechanical structure and high read/write speed. For instance, a solid-state drive utilizing a flash memory as a storage media has been widely applied in a computer host as a main hard disk for enhancing access efficiency of computer.
Generally, a memory storage device can establish a logical-physical mapping table to record a mapping relation between logical units and physical units, such that a host system can access data in the rewritable non-volatile memory module according to the mapping relation. Specifically, each time when the host system intends to write data into the memory storage device, it is possible that the logical units corresponding to the writing data and the logical units corresponding to the previous writing data belong to different logical-physical mapping tables. Therefore, the memory storage device can establish a mapping table for temporarily storing a physical-logical corresponding relation (a physical-logical mapping table) in order to program the writing data into one active physical erasing unit and temporarily store a mapping relation between the active physical erasing unit and the logical units corresponding to the writing data into said mapping table. For example, the conventional memory storage device can write the physical-logical mapping table corresponding to the physical erasing unit from a buffer memory into a fixed space preserved in the active physical erasing unit and update the logical-physical mapping table according to the physical-logical mapping table, so as to prevent the logical-physical mapping table from being frequently updated.
However, the data is usually compressed before being written into the rewritable non-volatile memory module, such that amounts of data actually programmed into the physical programming units may be different from one another. In other words, the size of the physical-logical mapping table for storing the mapping relation corresponding to the physical programming units may be different based on a result of the data compression. As such, in the case where the data is not compressed with a compression efficiency as expected, a waste of space may occur on the active physical erasing unit when the memory storage device writes the entire physical-logical mapping table corresponding to the active physical erasing unit into the fixed space preserved in the active physical erasing unit. Accordingly, it is one of the major subjects in the industry as how to prevent the waste of space for the physical erasing unit caused by the size of the physical-logical mapping table which dynamically changes according to the data compression, so as to effectively save a system resource of the rewritable non-volatile memory.
Nothing herein should be construed as an admission of knowledge in the prior art of any portion of the present invention. Furthermore, citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention, or that any reference forms a part of the common general knowledge in the art.